Continuous charges are also called current (or moving electrons). They are produced by a device called ‘a cell’.
Types of Cells
There are two types of cells. Namely:
- Primary cells
- Secondary cells.
A. Primary cells:
These are cells that cannot be recharged once they run down. E.g. torch batteries, calculator batteries, leclanche cell, Daniel cell. The components of the cell are shown
However, primary cells have two defects. They are:
- Polarization: This is a defect that results from the production of hydrogen bubbles around the copper plate of the cell. This will set up a back emf that reduces the emf in the external. As the cell works, hydrogen bubbles are released. These bubbles insulate the positive electrode and then slow it down. It could be minimized by brushing the plate or by using a depolarizer called manganese (iv) oxide (MnO2), Potassium tetraoxomanganese(IV) KMnO¬, Potassium Heptaoxodichromate (VI) K2Cr2O7… to oxidize the hydrogen bubbles to form water.
- Local Action: This defect results from not using a pure zinc plate which makes it to wear It is reduced by amalgamation i.e cleaning the zinc plate with H2SO4 and then rubbing it with mercury.
B. Secondary cells:
These are cells that could be recharged when they run down using a suitable battery charger. The two major types are lead acid accumulator and the nickel cadmium cell. E.g car batteries, motorcycle batteries, cell phone batteries and all other rechargeable batteries.
|Difference Between Primary Cell and Secondary Cell|
|Primary Cell||Secondary Cell|
|Slow discharge rate and have a high energy density.||Have a smaller energy density|
|It has high internal resistance||Low internal resistance|
|Dry cell because it has no fluid inside||There are made up of wet cells (flooded and liquid cells) and molten salt (liquid cells with different composition)|
|It has an irreversible chemical reaction||It has a reversible chemical reaction|
|Comes in a smaller and lighter design||More heavier and complex design|
|Its initial cost is cheap||Its initial cost is high|
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